Two chamber pumps and related methods

ABSTRACT

Two chamber pumps and related methods provide a platform for measuring flow rate in about real time without contacting the material being pumped. Pressure and optional temperature sensors disposed in a pressurized chamber allow for fluid delivery calculations after being calibrated or by knowing the initial volume of the fluid to be delivered.

BACKGROUND

The present disclosure relates to the field of pumps, especially thoseused to accurately dispense medication.

SUMMARY

Two chamber pumps and related methods provide a platform for measuringflow rate in about real time without contacting the material beingpumped. Pressure and optional temperature sensors disposed in apressurized chamber allow for fluid delivery calculations after beingcalibrated or by knowing the initial volume of the fluid to bedelivered.

According to a feature of the present disclosure, a device is disclosedcomprising a pressurizable first chamber, a second chamber for holding afluid, a flow lumen disposed exterior to the first chamber and in fluidcommunication with the second chamber, at least one pressure sensordisposed in the first chamber, and a flow controller disposed along theflow lumen. A pressurized substance in the first chamber is able tocause a: change of volume of the second chamber.

According to a feature of the present disclosure, a device is disclosedcomprising a pressurizable first chamber, a second chamber for holding afluid, a flow lumen disposed at least partially exterior to the firstchamber and in fluid communication with the second chamber, at least onepressure sensor disposed in the first chamber, a flow controllerdisposed along the flow lumen, and a microprocessor to compute at leastflow rate of fluid transferred through the flow lumen from the secondchamber. A pressurized substance in the first chamber is able to cause achange of volume of the second chamber by causing fluid to flow from thesecond chamber through the flow lumen and the microprocessor controlsthe flow controller.

According to a feature of the present disclosure, a method is disclosedcomprising providing a pump having: (a) a pressurizable first chamber,(b) a second chamber for holding a fluid, (c) at least one pressuresensor disposed in the first chamber, (d) a flow lumen in fluidcommunication with the second chamber, and (e) a flow controller. Apressurized substance in the first chamber is able to cause a change ofvolume of the second chamber.

DRAWINGS

The above-mentioned features and objects of the present disclosure willbecome more apparent with reference to the following description takenin conjunction with the accompanying drawings wherein like referencenumerals denote like elements and in which:

FIG. 1 is a cross sectional view of an embodiment of the pumps of thepresent disclosure having rigid outer casings;

FIG. 2 is a cross sectional view of an embodiment of the pumps of thepresent disclosure, where the outer casing of the pump is a collapsiblebag; and

FIG. 3 is a cross sectional view of an embodiment of the pumps of thepresent disclosure.

DETAILED DESCRIPTION

In the following detailed description of embodiments of the invention,reference is made to the accompanying drawings in which like referencesindicate similar elements, and in which is shown by way of illustrationspecific embodiments in which the invention may be practiced. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention, and it is to be understood that,other embodiments may be utilized and that logical, mechanical,biological, electrical, functional, and other changes may be madewithout departing from the scope of the present invention. The followingdetailed description is, therefore, not to be taken in a limiting sense,and the scope of the present invention is defined only by the appendedclaims. As used in the present disclosure, the term “or” shall beunderstood to be defined as a logical disjunction and shall not indicatean exclusive disjunction unless expressly indicated as such or notatedas “xor.”

According to the present disclosure, the term “real time” shall bedefined as the instantaneous state or lagging the instantaneous state bythe time taken to compute a measurement describing the instantaneousstate, provided the measurement computed reasonably approximates theinstantaneous state at the beginning of the measurement process and theinstantaneous state at the end of the measurement process.

The present disclosure discloses a pump that is able to measure flowrates or adjust flow rates in about real time. The pumps of the presentdisclosure comprise two chambers with at least a pressure sensordisposed therein to measure pressures in a pressured chamber that drivesflow of a fluid from a liquid chamber. Flow controllers are disposed aspart of the pump to either prevent flow or regulate and ensureconsistent flow rate. The operation of the pumps of the presentdisclosure maintain sterile conditions for the fluid flow from thepumps, while allowing for precise measurements for flow volumes withoutcompromising sterility.

According to embodiments and as illustrated in FIG. 1, pump 100comprises first chamber 110 and second chamber 120. First chamber is achamber that is pressurized such that the pressure in first chamberexceeds the pressure of second chamber. Consequently, when pump 100 isin an open state, flow of fluid contained in second chamber 120 iseffected.

Flow of fluid from second chamber is through flow lumen 130. Flow lumenmay be surgical or medical tubing, pipes, and other similar devicesdesigned for the flow of fluids from a source to a destination withoutappreciable loss of fluid.

According to embodiments, flow controller 140 may be disposed along flowlumen 130 to control flow. Control of flow, according to embodiments,may be an on/off type device, such as a clamp, whereby when flowcontroller is open flow is effected and when flow controller 140 isclosed, flow is prevented. Flow controller 140 may also comprise,according to embodiments, a flow restrictor to ensure constant orpredictable flow. According to embodiments, flow controller 140 maycomprise a plurality of flow restrictors, clamps, etc.

Fill device 150 is disposed along flow lumen 130 and facilitates thefilling of second chamber 120 with fluid. Fill device 150 may comprise aone-way valve, according to embodiments, whereby fluid is flowed throughvalve and into second chamber 120. Fill device 150 is a luer actuatedport, according to embodiments. According to optional embodiments, fillvalve comprises a device for putting a prefilled second chamber 120,such as a typical intravenous bag, into first chamber 110 after whichfirst chamber 110 is pressurized.

According to embodiments, and as shown in FIG. 1, first chamber 110 is achamber that is able to be pressurized. According to embodiments, firstchamber 110 may be made from any suitable rigid material, for examplepolycarbonate, ABS, or polyethylene. According to different embodiments,first chamber 110 may be made from flexible materials, for example PVC,polyethylene, silicon, polyurethane, or various rubbers. According toembodiments, first chamber 110 is sealed to prevent leakage of gascontained therein. According to embodiments, first chamber 110 may havea valve for repressurization or adjustment of pressure, as desired.According to embodiment and as illustrated in FIG. 2, first chamber 110comprises a bag-like or collapsible device.

Pressure sensor 115 is disposed in first chamber 100 to measure pressureat predetermined intervals, as well as initial pressure readings to beused to determine flow rate. Optionally, a temperature sensor may alsobe disposed in first chamber 100 to improve accuracy of flowmeasurement. Multiple pressure and temperature sensors may be used tomore accurately determine pressure and temperature in first chamber 110.

Second chamber 120, according to embodiments, comprises a collapsiblechamber that holds a fluid without appreciable leakage. When flowcontroller is in a state whereby flow is effected, flow from secondchamber is effected by the pressure differential between first chamber110 and second chamber 120. Second chamber may be made from PVC,polyisoprene, silicon, polyurethane, or other flexible materials.

According to embodiments and as shown in FIG. 3, second chamber 120 maybe defined by a collapsible or movable diaphragm 225. Rather thancollapsing second chamber 120, the movable or collapsible diaphragm 125is moved whereby flow is effected.

To dispense fluid from pump 100, a calibration step is necessary. Thecalibration step determines the initial volume of second chamber 120(V_(2i)), which is necessary to determine flow rate, as described belowusing the ideal gas law. According to embodiments, the most simplemethod for the determination of V_(2i) is to know the volume of fluidput into second chamber 120. This is accomplished by injecting a knownamount of fluid into second chamber 120 via fill device 150 or using adisposable second chamber 120 (i.e., an IV bag) holding a known volume.

According to embodiments, calibration may also be accomplished bycalculating, using the ideal gas law, the volume of second chamber 120from a known starting volume in an empty state. If second chamber 120occupies a known empty volume, for example using the pump of FIG. 3,wherein the diaphragm rests at a set position when second chamber 120 isempty, for example 0 ml or 10 ml, then prior to filling of secondchamber 120 with a fluid, the pressure and temperature of first chamberare measured. The initial volume of second chamber 120 is thencalculated after fluid is put into second chamber 120 using an equationto measure flow rate, which is derived in detail below:

$\begin{matrix}{V_{2\; {empty}} = \frac{P_{1\; i}{T_{1\; f}\left( {c - V_{2\; {filled}}} \right)}}{P_{1\; f}T_{1\; i}}} & (1)\end{matrix}$

For the purposes of the present application, second chamber 120 hasthree discrete states: empty, filled, and flowing. The empty statedefines second chamber when the volume is 0 or a known empty volume. Thefilled state defines the second chamber when it is filled with fluid.The flowing state defines a plurality of volumes where

V_(2filled)>V_(2flowing)>V_(2empty)  (2)

Typically, V_(2flowing) is representative of the state wherein fluid isbeing delivered from pump 100 to a patient, for example. However,V_(2flowing) may also be used for calculations during the filling ofsecond chamber 120 with fluid.

According to embodiments, flow is effected because the pressure of firstchamber 110 exceeds the fluid pressure in second chamber 120.Accordingly, flow rate may be calculated with high precision and inabout real time. Prior to determination of flow rate, the filled stateof pump 100 must be measured.

Calculation of flow rate is based on the ideal gas law, that is:

PV=nRT.  (3)

Because the total volume of pump 100 is known, that is the volume offirst chamber 110 (V₁) plus the volume of second chamber 120 (V₂) is aconstant, as shown:

V ₁ +V ₂ =c.  (4)

Thus, as fluid flows from V₂ to a delivery target, such as a patient,the volume of V₁ increases proportionally. Consequently, if V₁ isdetermined in a filled state and V₁ is determined in a flowing state ata time interval after fluid begins to flow from second chamber 120, thechange in volume of V₁ over the time interval t is the flow rate overthat time interval.

$\begin{matrix}{{flowrate} = {\frac{\Delta \; V_{2}}{\Delta \; t} = {\frac{\Delta \; V_{1}}{\Delta \; t}}}} & (5)\end{matrix}$

where Δt is the time interval over which ΔV₁ and ΔV₂ are measured.

However, the volume of second chamber (V₂) is not measured directly.Rather, changes in V₂ are measured indirectly from the changing volumeof V₁. Measurements of the volume of V₁ are accomplished with pressuresensor and optional temperature sensor.

Turning again to the ideal gas law, because first chamber 110 is sealed,the number of molecules (n) of gas in first chamber 110 remainsconstant. Additionally, R is constant. Therefore,

nR=k  (6)

where k is a constant. Thus,

$\begin{matrix}{{PV} = {kT}} & (7) \\{\frac{PV}{T} = {k.}} & (8)\end{matrix}$

Because first chamber 110 is sealed, k remains constant throughout theflow of fluid from second chamber 120. Additionally, pressure sensor andoptional temperature sensor disposed in first chamber 110 allows formeasurement of P_(1filled), P_(1flowing), T_(1filled), and T_(1flowing).Finally, the filled volume (V_(2filled)) of second chamber 120 is known,which allows calculation of V_(1filled), and therefore calculation ofV_(1flowing). The following equation for first chamber 110 results:

$\begin{matrix}{\frac{P_{1\; {filled}}V_{1\; {filled}}}{T_{1\; {filled}}} = {\frac{P_{1\; {flowing}}V_{1\; {flowing}}}{T_{1\; {flowing}}}.}} & \left( {9a} \right)\end{matrix}$

Artisans will understand the filled state comprises the end state ateach discrete time interval in which flow rate is measured. Indeed,according to embodiments, the filled state of the prior time intervalmay comprise the filled of the succeeding time interval, and so forth asshown as the alternative to equation (9a).

$\begin{matrix}{\frac{P_{1\; {flowing}_{\tau = x}}V_{1\; {flowing}_{\tau = x}}}{T_{1\; {flowing}_{\tau = x}}} = {\frac{P_{1\; {flowing}_{\tau = {x + y}}}V_{1\; {flowing}_{\tau = {x + y}}}}{T_{1\; {flowing}_{\tau = {x + y}}}}.}} & \left( {9b} \right)\end{matrix}$

where τ is a time interval, when x=0, the flowing state is equal to thefilled state, and y≧1 time interval. Artisans will readily appreciatethat τ or Δt may represent the aggregate time from the start of flow offluid from second chamber 120 to the time being measured or may beindicative of any arbitrary time interval after the start of flow offluid from second chamber 120 to the time being measured.

To more clearly illustrate the principle of determining ΔV₁, temperaturewill be assumed to be constant for the purposes of the next set ofequations. Thus,

P_(1filled)V_(1filled)=P_(1flowing)V_(1flowing).  (10)

Therefore, solving for V_(flowing) of first chamber 110 yields

$\begin{matrix}{V_{1\; {flowing}} = {\frac{P_{1\; {filled}}V_{1\; {filled}}}{P_{1\; {flowing}}}.}} & (11)\end{matrix}$

However, V_(1filled) is unknown and must be calculated from the totalvolume of pump c and from knowing the filled volume (V_(2filled)) offluid put into second chamber 120:

V _(1filled) =c−V _(2filled)  (12)

Thus, the total amount of volume flowed may be calculated using theequation, based on the proportionality of flow between first chamber 110and second chamber 120:

$\begin{matrix}{{flowrate} = {\frac{V_{2\; {flowing}} - V_{2\; {filled}}}{\Delta \; t} = {\frac{V_{1\; {flowing}} - V_{1\; {filled}}}{\Delta \; t}}}} & (13)\end{matrix}$

Thus, to determine V_(1flowing), we can use the relationship expressedin equation (ii). As V_(1filled) is unknown, substituting known valuesof c and V_(2filled), the following equation results:

$\begin{matrix}{V_{1\; {flowing}} = {\frac{P_{1\; {filled}}\left( {c - V_{2\; {filled}}} \right)}{P_{1\; {flowing}}}.}} & (14)\end{matrix}$

Using equation (13) and based on the fact thatV_(2flowing)=|−(V_(1flowing))|, flow rate may be calculated as

$\begin{matrix}{{flowrate} = {{\frac{\frac{P_{1\; {filled}}\left( {c - V_{2\; {filled}}} \right)}{P_{1\; {flowing}}} - V_{1\; {filled}}}{\Delta \; t}}.}} & (15)\end{matrix}$

Adding temperature back to the equation allows for a more precisemeasurement of flow rate and is easily accomplished:

$\begin{matrix}{{flowrate} = {{{\frac{\frac{P_{1\; {filled}}\left( {c - V_{2\; {filled}}} \right)}{P_{1\; {flowing}}} - V_{1\; {filled}}}{\Delta \; t}\left( \frac{T_{1\; {flowing}}}{T_{1\; {filled}}} \right)}}.}} & (16)\end{matrix}$

According to embodiments, measurements of flow rate are taken atdiscrete time intervals. These time intervals may range from manymeasurements per second to measurements taken over the course ofminutes, hours, or days, depending on the specific application.Accordingly, measuring flow rate provides about real-time feedback,which may be used to adjust flow rate. By coupling the measurement offlow rate to flow controllers, flow may be closely regulated. Forexample, if flow controller 140 comprises a clamp, then feedback systemmay open the clamp when additional flow of fluid is needed and close theclamp when too much flow has occurred. Thus, the combination of a flowcontroller and the about real-time flow measurement provides a platformto deliver measurably accurate volumes of a fluid.

According to embodiments, first chamber 110 may be made from expandablematerials. In such embodiments, first chamber 110 may be a disposablebag or similar flexible-type container such as an IV-type bag, that tendto expand or contract depending on the pressure within the firstchamber. Thus, the above equations must account for the effectsexpansion or contraction due to change of pressure within first chamber110. In other words, as pressure increases, the volume within firstchamber 110 will change in a predictable way and visa versa. Forexample, by including in the calculations a factor incorporating themodulus of elasticity of the material from which first chamber 110 ismade into the V₁, the change in the volume of first chamber 110 isreasonably predictable.

Accuracy of the determination of the change in V₁ attributable to theelasticity of the material from which first chamber is made is improvedby calibrating the system at a known initial pressure of first chamber110 and volume of second chamber 120. Thus, first chamber 110 isdesigned and made to have a known volume in this initial state. Aspressure increases, the calculated additional volume due to expansion offirst chamber 110 may be added to the initial volume to derive anaccurate value of V₁.

Referring again to the calibration step, as the pressure of secondchamber 120 increases as it is charged with the fluid, the volume offirst chamber 110 is decreased and the pressure within first chamber 110increases. At the same time, because first chamber 110 is made fromnon-rigid materials there will be predictable expansion of thedimensions of first chamber 110, with increased resulting volume. Thus,to determine the actual volume of first chamber 110 after the initialstate, the pressure of first chamber is measured and volume iscalculated as described previously, taking into account the incrementalvolume increase or decrease of first chamber 110 observed due toelasticity of material from which first chamber 110 is made.

According to alternative-type embodiments, a method for accounting forthe change in V₁ due to expansion or contraction of first chamber 110 isto lookup the approximate change in volume of first chamber 110 aspressure within first chamber 110 increases or decreases in a lookuptable. The lookup table, according to embodiments, is based uponaveraged value for a plurality of the same first chamber 110 having thesame dimensional parameters and will provide a reasonably approximatefactor to add or subtract to V₁ at a plurality of given measuredpressures.

These principles are illustrated in the following equations. Let V₁ ^(E)be the supplemental volume of first chamber as first chamber 110 expandsor contracts. In systems where first chamber 110 is made from rigidmaterials, the volume of first chamber 110 plus the volume of secondchamber 120 is constant, as expressed in equation (4).

V ₁ +V ₂ =c  (4)

In system where first chamber 110 is made from expandable materials,however, a factor must be added to c denoting the added or lost volumeoccurring due to expansion or contraction of the first chamber 110.

V ₁ +V ₂ =c+V ₁ ^(E)  (17)

Thus, the volume of V₁ may be calculated as:

V ₁ =c+V ₁ ^(E) −V ₂.  (18)

Thus, in systems where first chamber 110 is made from expandablematerials, equation (16) is modified to account for the expanded firstchamber 110:

$\begin{matrix}{{flowrate} = {{{\frac{\frac{P_{1\; {filled}}\left( {c + V_{1}^{E} - V_{2\; {filled}}} \right)}{P_{1\; {flowing}}} - V_{1\; {filled}}}{\Delta \; t}\left( \frac{T_{1\; {flowing}}}{T_{1\; {filled}}} \right)}}.}} & (19)\end{matrix}$

Artisans will readily recognize that V₁ ^(E) may be calculated if themodulus of elasticity is known or may be simply recorded as a set ofvalues within a table for quick lookup, especially in situations where amicroprocessor is not designed to perform series of complex calculationsor where power consumption is an issue.

While the apparatus and method have been described in terms of what arepresently considered to be the most practical and preferred embodiments,it is to be understood that the disclosure need not be limited to thedisclosed embodiments. It is intended to cover various modifications andsimilar arrangements included within the spirit and scope of the claims,the scope of which should be accorded the broadest interpretation so asto encompass all such modifications and similar structures. The presentdisclosure includes any and all embodiments of the following claims.

1. A device comprising: a pressurizable first chamber; a second chamberfor holding a fluid; at least one flow lumen in fluid communication withthe second chamber; at least one pressure sensor disposed in the firstchamber; and a flow controller disposed along the flow lumen; amicroprocessor for computing flow rate from data provided by thepressure sensor; wherein a pressurized substance in the first chambereffects a change of volume of the second chamber; and wherein themicroprocessor controls the flow controller.
 2. The device of claim 1,further comprising a fill port for filling the second chamber with thefluid.
 3. The device of claim 1, further comprising at least onetemperature sensor disposed in the first chamber.
 4. The device of claim1, wherein the flow controller is a clamp.
 5. The device of claim 1,wherein the flow controller is a flow restrictor.
 6. The device of claim1, wherein the first chamber is pressurized prior to filling the secondchamber with the fluid.
 7. The device of claim 1, wherein the firstchamber is made from an expandable material.
 8. The device of claim 7,wherein the expansion of the expandable material is a function of thepressure of the first chamber.
 9. A device comprising: a pressurizablefirst chamber; a second chamber for holding a fluid; at least one flowlumen in fluid communication with the second chamber; at least onepressure sensor disposed in the first chamber; a flow controllerdisposed along the flow lumen; and a microprocessor to compute at leastflow rate of fluid transferred through the at least one flow lumen fromthe second chamber; wherein a pressurized substance in the first chambereffects a change of volume of the second chamber whereby the fluid flowsfrom the second chamber through the flow lumen; and wherein themicroprocessor controls the flow controller.
 10. The device of claim 9,further comprising a fill port for filling the second chamber with thefluid.
 11. The device of claim 9, further comprising at least onetemperature sensor disposed in the first chamber.
 12. The device ofclaim 9, wherein the flow controller is a clamp.
 13. The device of claim9, wherein the flow controller is a flow restrictor.
 14. The device ofclaim 9, wherein the first chamber is pressurized prior to filling thesecond chamber with the fluid.
 15. The device of claim 9, furthercomprising at least one temperature sensor; wherein the microprocessorgathers data from the temperature sensor to compute the at least a flowrate of fluid transferred through the flow lumen from the secondchamber.
 16. A method comprising: providing a pump having: (a) apressurizable first chamber; (b) a second chamber for holding a fluid;(c) at least one pressure sensor disposed in the first chamber; (d) aflow lumen in fluid communication with the second chamber; and (e) aflow controller; wherein a pressurized substance in the first chamber isable to cause the fluid to flow from the second chamber and through theflow restrictor thereby changing the volume of the second chamber. 17.The method of claim 17, further comprising providing at least onetemperature sensor disposed in the first chamber.
 18. The method ofclaim 17, wherein the flow controller is a clamp.
 19. The method ofclaim 17, wherein the flow controller is a flow restrictor.
 20. Themethod of claim 17, further comprising a microprocessor for computingflow rate from data provided by the pressure sensor; wherein themicroprocessor controls the flow controller.